Plastic components used in automobile cooling systems through which an engine cooling fluid flows are required to use a plastic having satisfactory productivity, resistance to hydrolysis, satisfactory resistance to calcium chloride with respect to cracks caused by exposure to calcium chloride, and satisfactory toughness and the like.
Therefore, in the prior art, glass-reinforced polyamide 6,6 compositions reinforced with glass fiber, and glass-reinforced polyamide compositions containing a blend of polyamide 6,6 and polyamide 6,12, having better resistance to cracking caused by exposure to calcium chloride, for example, have been used to produce automobile cooling system components.
On the other hand, Japanese Unexamined Patent Publication No. 10-219107 describes a plastic used for the purpose of use in fields such as automobile and mechanical components, and more specifically, a glass-reinforced polyamide composition that uses various polyamide resins which are usually used as engineering plastics.
Incidentally, engine cooling fluids are being expected to function at higher temperatures in response to a demand for automobiles having better fuel efficiency. However, in automobile cooling system components in which glass-reinforced polyamide compositions are used, rises in temperature of the engine cooling fluid can accelerate the rate of deterioration of the polyamide composition due to hydrolysis, thereby requiring a higher resistance to hydrolysis than in the prior art. In addition, long-term exposure of polyamide compositions to high-temperature fluid can lead to creep and other undesirable deformations of automobile cooling system components, thereby resulting in the need for higher levels of toughness and resistance to high-temperature creep than in the prior art.